Arc control apparatus for load-break switches



April 29, 1969 J. w. ERICKSON 3,441,699

ARC CONTROL APPARATUS FOR LOAD-BREAK SWITCHES Filed May 27, 1968 Sheetof 2 //vv/vr0/?. JOHN W ERIC/(SON April 29, 1969 J. w. ERICKSON3,441,699

ARC CONTROL APPARATUS FOR LOAD-BREAK SWITCHES Sheet of2 Filed May 27,1968 ar y nited States Patent US. Cl. 200-144 8 Claims ABSTRACT OF THEDISCLOSURE Arc control apparatus for a load-break switch having amovable contact that is movable along a given path into and out ofengagement with a stationary contact; the arc control apparatuscomprises an arc-quenching chute including a plurality of metal gridplates slotted to receive the movable contacts, the backs of the gridplates being closed by a back member formed of a material that releasesa deionizing gas in the present of an arc, with apertures in the backmember permit-ting escape of'gases but precluding recombination of theare behind the chute. An end grid plate of degassing material is alsoused. A separate arcing contact of spring construction backed up by asupport member prevents arching between the main switch contacts.

Cr0ss-references to related applications This application .is acontinuation-in-part of application Ser. No. 542,937, filed Apr. 15,1966, now abandoned.

Background of the invention Load-break pressure contact switches forservice entrance and like applications in which the switch may be openedor closed under fault conditions must withstand extremely high currents.Typical low voltage switches of this kind (usually 240 or 480 volts),although nominally rated for currents between 100 and 4000 amperes, maybe required to withstand fault currents substantially in excess of100,000 amperes. When a switch of this kind is actuated under faultconditions, an arc of extremely high current is established between theswitch contacts. This frequently results in severe pitting of the switchcontacts or even destruction of the switch. There is also a substantialpossibility of fire or explosion if the arc is not extinguished almostimmediately.

Conventional practice is to provide a multiple-chamber arc chute, alongthe path of movement of the movable switch contact, that separates thearc into segments and thus accelerate extinction of the arc. Some arechutes of this kind include side wall members that generate a deionizinggas, in the presence of an arc, to assistant in extinction of the arc.Nevertheless, substantial difficulty is still encountered even whereconventional arc chutes are employed, particularly in switches of higheramperage ratings.

It has also been known to provide arcing contacts, 1n switches of thiskind, that are physically separate from, though electrically connectedto the stationary contacts of the switch. A separate arcing contact aidsmaterially in reducing pitting of the main switch contacts. Furthermore, in conventional bolted pressure contact switches, the use of aseparate arcing contact eliminates the necessity for maintaining adragging engagement between the movable and stationary contacts of theswitch during intervals in which the switch is being opened or closed,so that the switch can be thrown more rapidly then would otherwise bepossible. But a separate arcing contact can 3,441,699 Patented Apr. 29,1969 also interfere with operation of the switch if firmly engaged withthe movable switch contact during opening and closing movements. On theother hand, if loose engagement or even some separation is permitted,there may be excessive pitting or other damage to the arcing contact.

Summary of the invention It is an object of the present invention,therefore, to provide a new and improved arc control apparatus for aload-break switch that comprises an arc-quenching chute of themultiple-chamber type affording improved efiiciency in operation yetconstructed of inexpensive materials and affording an economic assembly.

A more specific object of the invention is to provide a multichamber arcchute construction that allows dissipation of gases from the arc chutechambers while at the same time preventing recombination of the areexternally of the chute.

A further object of the invention is to provide an arc control apparatusthat includes an arc chute that makes effective use of materials thatproduce deionizing gases during the arcing attendent upon opening andclosing of a load-break switch under fault conditions, yet whichmaintains the strength and rigidity of met-a1 construct-ion.

An additional object of the invention is to provide a new and improvedarc control apparatus for a load-break switch that comprises an arcingcontact that is independent of the stationary cont-act of the switch andthat is capable of diverting the are produced on opening or closing ofthe switch from the stationary contact without engendering excessivepitting or potential damage to the arcing contact itself.

Accordingly, the invention relates to an arc control apparatus for aload-break switch employed in service entrance and like applications inwhich the switch may be opened or closed under fault conditions, theswitch including a stationary contact and a movable contact that ismovable along a given path into and out of engagement with thestationary contact. The arc control apparatus of the invention comprisesa pair of opposed side frame members mounted in spaced relation to eachother on opposite sides of the aforesaid path with a plurality of metalgrid plates spanning the space between the frame members and forming aplurality of chambers subdividing the are developed upon opening orclosing of the switch. Each of these grid plates has a generallyV-shaped opening in its forward edge through which the movable contactpasses during its opening and closing movements. A back member, formedof a material that releases a deionizing gas in the presence of an arc,extends between the frame members behind the grid plates to close theback of each arc-dividing chamber. Preferably, this back member has aplurality of individual openings individual- 1y aligned with the arcdividing chambers but staggered from side-to-side of the assembly toallow release of gases from the chambers without permittingrecombination of the arc. The apparatus further includes an end gridplate of substantially the same configuration as the metal grid platesand spanning the end of the frame members remote from the stationarycontact of the switch, this plate also being formed of a material whichreleases a deionizing gas in the presence of an arc. An arcing contact,separate from the stationary contact, is located at the base end of theapparatus and constitutes a spring contact member backed up by a rigidsupport member with the contact member positioned to engage the end ofthe movable switch contact.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, shows preferredembodiments of the present invention and the principles thereof and whatis now considered to be the best mode contemplated for applying theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be made as desired by those skilled in the artwithout departing from the present invention.

Brief description 07 the drawings FIG. 1 is a front elevation view of anarc-quenching chute incorporated in an arc control apparatus constructedin accordance with one embodiment of the invention;

FIG. 2 is a sectional view, taken approximately along line 22 in FIG. 1,of one pole of a load-break switch equipped with are control apparatusconstructed in accordance with the invention;

FIG. 3 is a plan view of the arc-quenching chute of FIG. 1;

FIG. 4 is a rear elevation view of the arc-quenching chute of FIG. 1;

FIG. 5 is an elevation view of one pole of a 1oadbreak switch equippedwith are control apparatus constructed in accordance with anotherembodiment of the invention; and

FIG. 6 is a detail sectional view taken approximately along line 66 inFIG. 5.

Description of the preferred embodiments FIGS. 1-4 illustrate an arccontrol apparatus for a load-break switch, including an arc-quenchingchute 10, constructed in accordance with one embodiment of the presentinvention. As shown in FIG. 2. the load-break switch includes a movablecontact 11 formed by two blades, only one of the blades beingillustrated in the drawing. In FIG. 2, the switch is shown in closedposition, with the movable contact 11 engaging a fixed or stationarycontact 12. The movable contact 11 and stationary contact 12 maycomprise elements of a load-break boltedpressure switch of the kinddescribed in U.S. Patent No. 3,213,247, with the two blades of themovable contact 11 being firmly bolted in pressure engagement with thestationary contact 12 by means of a clamping bolt 19 when the switch isclosed. A more detailed explanation of a typical bolted pressure contactswitch construction is provided hereinafter in connection with FIG. 5.It should be understood that the present invention is capable of usewith many dilferent electrical switch sizes and with a variety ofdifferent contact constructions and that the particular constructionadopted for the switch or circuit breaker contacts is subject tosubstantial variation.

The movable switch contact 11 is pivotally mounted upon a pivot pin 13for counterclockwise rotation from the closed position of FIG. 2 to anopen position in which the movable contact is displaced from stationarycontact 12. Spanning the tip end of the movable contact 11, between thetwo contact blades, is a contact block 14 which is a part of the movablecontact structure. Contact block 14 is positioned for intermediatesliding engagement with a separate arcing contact 15 that iselectrically connected to stationary contact 12. When the switch is infully closed or fully open positions, block 14 is free of arcing contact15; engagement therebetween occurs only during opening and closingmovements of the switch. Arcing contact 15 is mounted upon a resilientconductive support member 16 secured by appropriate fasteners 17 to twoconductive bars 18 which are in turn mounted on the stationary contact12 of the switch.

From the foregoing, it will be seen that to open the illustrated pole ofthe switch, the blades of movable contact 1-1 are pivoted in acounterclockwise direction about pin 13. During the early part of thispivotal movement, as the movable contact blades move forwardly alongstationary contact 12, contact block 14 engages arching contact 15.Block 14 remains engaged with arcing contact 15 as the contact bladesmove free of the stationary contact of the switch. Thus, continuouselectrical contact is maintained until the free end of the movablecontact, block 14, is well into the arc-quenching chute 10. If theswitch is operating properly and there is no fault in the electricalcircuit connected to stationary contact 12, only a relatively weak arcis drawn between contact block 14 and arcing contact 15 at the timeblock 14 moves free of the arcing contact and the switch is actuallyopened.

On the other hand, if there is a fault in the circuit controlled by theswitch, it is possible that extremely highcurrent are may be formed. Thefault current may reach values well in excess of 100,000 amperes. Underthese conditions, the separation of movable contact 11 from stationarycontact 12, and more particulary the subsequent separation of contactblock 14 from arcing contact 15 results in an extremely high-currenthigh-temperature are between contact members 14 and 15, within thearcquenching chute 10. The arc-quenching chute 10 must function todivide and extinguish this arc, preferably in less than one-half cycle,in order to avoid extreme damage to the switch and to prevent a possiblefire or explosion.

The arc-quenching chute 10 includes a pair of opposed side frame members20 and 21 of dielectric material disposed in spaced relation to eachother on opposite sides of the arcuate path followed by the movablecontact 11 during opening and closing operations of the switch. Aplurality of metal grid plates 22 are mounted between frame members 20and 21. Grid plates 22 are usually made of steel, although other metalsmay be used if desired. Grid plates 22 are aligned in spaced relation toeach other and form a series of slots or chambers 23 between adjacentgrid plates. Thus, as the are between contact block 14 and arcingcontact 15 is drawn out with continuing movement of the movable contactof the switch, the arc is subdivided into a plurality of isolatedportions.

The subdivided arc tends to expand through the chambers 23 and torecombine at the rear of the grid plates 22, particlarly under highfault conditions. Recombination of the arc externally of thearc-quenching chute 10 is eifectively prevented by a back plate 25 (seeFIGS. 2 and 4) that is mounted between the side frame members 21 and 22and that closes off the rear portion of each of the individual arcchambers 23.

A completely solid and continuous back plate 25 creates a possibilityand likelihood that, under fault conditions, the arc will be forcedforwardly out of the chambers 23 and will be established between themovable switch contact comprising the blades 11 and the stationarycontact 12. This is prevented by .providing back plate 25 with aplurality of individual openings 26. Openings 26 permit part of the heatand gas created by the arc in the individual chambers 23 to pass throughthe back plate 25 and prevent the are from being blown out frontwardlyof the chambers 23.

As shown in FIGS. 2 and 4, each of the apertures 26 in back plate 25 isaligned with a respective one of the chambers 23 and relieves pressurefrom that one chamber only. Furthermore, the individual apertures 26 arenot as wide as the back portions of the related chambers 23 and do notpermit the arc to blow completely out of the back portion of thearc-quenching chute. Instead, the apertures 26 are staggered fromside-to-side of the chute 10 and each extends for less than one-half ofthe width of the back plate 25. Thus, back plate 25 blocks theindividual arc-quenching chambers on a staggered basis that preventsrecombination of the arc segments in series behind the arc chute. Withthe illustrated construction adequate pressure relief is obtainedwithout recombination of the are behind the arc chute.

Back plate 25 and side plates 20 and 21 are each formed of a plastic,ceramic, hardboard, or even paperboard material which, when subject tohigh temperature, generate a deionizing gas that aids materially inextinction of the arc. A number of suitable and well-known refractories,plastics, and hardboard materials are commercially available that may beemployed in the fabrication of the side frame members 20 and 21 and backmember 25. Preferably, side frame members 20 and 21 are made of a moldedplastic material for economy and efficiency in production. Thedeionizing gases developed by the side plates 20 and 21 and the backplate 25, particularly under the high temperatures developed ininterruption of fault currents, aid materially in extinguishing the arc.1

Another element in the arc-quenching chute that aids materially inpreventing continuation of the are upon opening of the movable switchcontact is the endmost grid plate 30, FIGS. 1, 2 and 3. Grid plate 30 isnot formed of metal. Instead, it is fabricated from a suitable plastic,ceramic, or hardboard material that generates deionizing gas whensubject to the high temperatures of an electrical arc. Two or more ofthe end grid plates can be constructed of such material, but one isusually adequate.

As best seen in FIG. 1, the preferred configuration for the end plate 30is one which is identical to the metal grid plates 22. In the preferredconstruction, the metal grid plates 22 are stamped or punched from sheetsteel. In a like manner, the end plates 30 maybe punched to the sameconfiguration from a sheet of plastic or hardboard material, using thesame dies. Moreover, the thickness of the end grid plate 30 ispreferably the same as the steel grid plates 22.

As shown in FIGS. 1 and 3, grid plates 22 and 30 are relatively flatplates each formed with a V-sha-ped opening of decreasing size fromtheir forward edges 34 toward a rear central surface 35. Moreparticularly, the openings in the grid plates 22 and 30 each comprise apair of converging oblique edges 36 and. 37 leading to rounded surfaces38 and 39 terminating in the rounded surface 35. The shape of theopenings in each of the grid plates 22 and 30 is dimensioned to surroundthe tip portion of the movable switch contact, comprising block 14, onthree sides without contacting the block, thereby providing a wraparoundarc chute for the switch. As seen in FIG. 2, grid plates 22 and 30 arearranged in an arcuate configuration along radial lines from the pivotalaxis of the movable switch contact (pivot pin 13) to surround the outerends of the movable switch contact 11 as the latter moves along itsarcuate path in opening or closing of the switch. This constructionassures isolation of the arc, upon actuation of the switch, within thechambers 23 where it is divided and extinguished.

For convenience of assembly, side frame members 20 and 21 are eachprovided with a series of slots or openings for receiving the endportions of the side walls of the grid plates 22 and 30 to hold the gridplates in their mounted position between the side frame members of thearc-quenching chute. Back plate 20is held in position against therearward portions of the grid plates by two generally U-shaped shoulderor mounting members 40 and 41 that are a part of the side frame members20 and 21, respectively. Thus, each mounting member has an uppergenerally right-angle leg 45 extending over the top grid plate 30 and alower leg 46 extending beneath the lower grid plate 22. Mounting members40 and 41 are shown as separate elements in the drawing but may beformed integrally with the respective side frame members 20 and 21.

Grid plates 22 and 30 and back plate 25 are all locked into the assemblycomprising arc-quenching chute 10 by means of a pair of tie members 46and 47 that extend between the side frame members 20 and 21 of thechute. Nuts 48 and 49 threaded onto the tie members hold the completeassembly together in rigid relationship. Manifestly, other kinds ofmounting or securing means can be employed in lieu of bolts 46 and 47.For example,

grid plates 22 may themselves include fasteners extending through theopposed side frame members 20 and 21 and crimped to provide a rigidassembly. The illustrated construction is preferred, however, since itavoids any necessity for individual fastening of the grid plates to theside frame members.

Arc chute 10 can be mounted independently of the electrical portion ofthe switch. However, in the preferred construction illustrated in FIGS.1-4, the arc chute is directly mounted upon a part of the stationarycontact for the switch. More specifically, the side frame members 20 and21 include dependent fingers 50 and 51 formed with opposed pairs ofintegral bosses extending toward one another. An upper pair of bosses 52and 53 and a lower pair of bosses 54 and 55 on the side frame membersreceive bolts 60 and 61, respectively, to mount the arc-quenching deviceon the spaced bars 18 that support the arcing contact 15 and thatconstitute a part of the stationary contact of the switch.

With electrical switches of different ratings, the size and shape ofgrid plates 22 and 30 may be changed. However, the side frame members 20and 21 may be utilized for a relatively large range of switch ratingswithout modification. More specifically, side frame members 20 and 21 ofa given specific size may be readily employed with switches encompassinga wide range of voltage and current ratings (e.g., 120 to 480 volts andto 1200 amperes) merely by changing the size of the grid plates.

FIGS. 5 and 6 illustrate a single pole of a load-break switch thatincorporates a modification of the arc control apparatus of the presentinvention. The movable contact 11 of the switch comprises two pairs ofmovable contact blades; only one blade appears in FIG. 5 but segments ofeach are illustrated in FIG. 6, being designated as blades 11A, 11B, 11Cand 11D. As before, the movable blade contact is pivotally mounted uponthe pivot pin 13. FIG. 5 illustrates a part of the operating mechanismfor the switch, typical of construction used in bolted pressure contactswitches.

The operating mechanism of the switch as shown in FIG. 5 comprises acrank 101 that is pivotally mounted upon pin 13, rotation of crank 101being independent of pivotal movement of the blades 11A-11D forming themovable contact 11 of the switch. Crank 101 is pivotally connected by apin 102 to a link 103 with the opposite end of link 103 being pivotallyconnected by a pin 104 to a lever 105. The lever 105 is afiixed to thebolt 19 that extends across the movable contact 11 of the switch betweenthe two pairs of contact blades. Bolt 19 is threaded into two nuts (notshown) that are aflixed to the outside blades of the movable contactassembly. A spring 106 is connected between link 103 and the innercontact blades.

In the construction illustrated in FIGS. 5 and 6 the arcquenching chute10 is utilized without substantial change from the embodiment describedabove. It includes the side frame members 20 and 21 mounted upon anextension portion 112A of the stationary contact 112, which in thisinstance is of hollow squared-cylinder construction. Inasmuch as thearc-quenching chute is the same as described above in connection withFIGS. 1-4, it is not shown in detail in FIGS. 5 and 6.

The embodiment of FIGS. 5 and 6 further includes an arcing contact 115mounted upon a resilient conductive arm 116 that is aflixed to thestationary contact extension 112A. As before, the arcing contact ispositioned to engage a contact block 14 mounted between the tip ends ofthe movable blades of contact 11. In this instance, however, the arcingcontact is provided with a rigid support member 121 mounted behind thearcing contact in position to limit movement of the arcing contact awayfrom the movable contact of the switch.

In opening of the switch, crank 101 is rotated in a clockwise directionabout pin 13. The initial movement of the crank pulls link 103 to theleft and pivots lever 105 in a counterclockwise direction. This rotatesbolt 19 and releases the clamping pressure that presses the two pairs ofmovable contact blades against the legs of the stationary contact 112when the switch is closed. Continuing movement of crank 101, afterunbolting of the switch, pivots movable contact 11 in a counterclockwisedirection about pivot pin 13 to open the switch in the manner describedabove in relation to the embodiment of FIGS. 1-4.

During opening and closing movements of the switch it is quite importantthat little or no mechanical drag be applied to the contacts. As theswitch opens, contact block 14 on the movable cointact engages arcingcontact 115. The relatively light pressure exerted by the spring arm 116upon which the arcing contact is mounted does not interfere to anyappreciable extent with the opening and closing movements of the switch.This makes it possible to open and close the switch rapidly, minimizingarcing within the switch and reducing pitting of all contacts includingthe arcing contact.

If the switch is opened or closed under fault conditions, the highcurrent are produced between contact block 14 and arcing contact 115forcibly drives the arcing contact away from block 14. With a spring 116that is light enough to permit rapid actuation of the switch, asdescribed above, the force applied to the arcing contact may be greatenough to deform the arcing contact mount or even break it offcompletely. The result may be permanent damage to the stationary contact112 through excessive arcing between the main Contacts of the switch,since the arcing contact 115 is no longer availavle for protection.Thus, it may become necessary to replace the arcing contact and theswitch operator may not immediately recognize this requirement.

This difficulty is obviated by the use of the support 121 mounted closebehind arcing contact 115. The relatively heavy and rigid support 121interrupts the backward movement of arcing contact 115, under faultconditions, before the arcing contact can move far enough to elfect apermanent deformation of its spring 116. Consequently, a relativelylightweight spring 116 can be used safely without substantial likelihoodof damage to the arcing contact or any other portion of the switch asthe result of opening or closing of the switch under fault conditions,while at the same time avoiding excessive drag on the switch for normalopening and closing movements. The illustrated construction providesmuch freer movement of the switch than is possible with moreconventional arrangements in which arcing contacts are engaged bypressure between the switch blades in a manner similar to that utilizedin conjunction with the prinicpal stationary contact of the switch.

Hence, while preferred embodiments of the invention have been describedand illustrated, it is to be understood that they are capable ofvariation and modification.

I claim:

1. In a load-break switch for service entrance and like applications inwhich the switch may be opened or closed under fault conditions, saidswitch including a stationary contact and a movable contact, saidmovable contact being movable along a given path into and out ofengagement with said stationary contact to open and close the switch,arc control apparatus comprising:

a pair of opposed side frame members disposed in spaced relation to eachother on opposite sidesof said path;

a plurality of metal grid plates spanning the space between said framemembers to form a plurality of chambers subdividing the arc developedupon openin g or closing of the switch,

each of said grid plates having a generally V-shaped opening in itsforward edge through which said movable contact passes during itsopening and closing movements;

a back member extending between said frame members and disposedrearwardly of said grid plates to close the back of each of saidchambers, said back member being formed of a material which releases adeionizing gas in the presence of an arc;

and an end grid plate of substantially the same configuration as saidmetal grid plates, spinning the end of said frame members remote fromsaid stationary contact, formed of a material which releases adeionizing gas in the presence of an arc.

2. Arc control apparatus for a load-break switch according to claim 1 inwhich said back member has a plurality of individual openings extendingtherethrough, each opening being aligned with a respective one of saidchambers, said openings each extending for less than onehalf the widthof its associated chamber and said openings being staggered alternatelyfrom side-to-side of said apparatus to allow dissipation of heat and gasfrom the chambers without recombination of the arc externally of thechambers.

3. Are control apparatus for a load-break switch according to claim 1 in:which said side frame members each includes a plurality of slots forreceiving and aligning said grid plates in an arcuate array, saidapparatus further including at least two tie members extending acrosssaid device between said side frame members for securing said side framemembers, said back member, and said grid plates together in a rigidassembly.

4. Arc control apparatus for a load-break switch according to claim 3and further including a pair of mounting members, one of said mountingmembers extending along each of said side frame members in engagementwith the edge portion of said back member to clamp said back memberbetween said mounting members and said grid plates.

5. Arc control apparatus for a load-break switch according to claim 1 inwhich said grid plates are aligned in an arcuate array and are disposedalong radial lines from the pivot point of an arcuately movable switchcontact with the forward edges of the grid plates spaced more closelyadjacent to one another than the rearward ends of the grid plates and inwhich said openings in said forward edges of said grid plates define aconvergent arcuate passageway for said movable contact.

6. Arc control apparatus for a load-break switch according to claim 1and further including a resilient arcing contact electrically connectedto but spaced from the stationary contact of said switch, located alongthe path of said movable switch contact in position to engage the endportion of said movable contact with only a light pressure over aportion of said path that overlaps the separation of the movable contactfrom said stationary contact on opening of the switch.

7. Arc control apparatus for a load-break switch according to claim 6 inwhich said arcing contact is a cantilever spring supported contactpositioned adjacent one end of said movable contact and furthercomprising an auxiliary support member mounted adjacent said arcingcontact on the opposite side thereof from said movable contact inposition to limit movement of said arcing contact away from said movableswitch contact in the presence of high fault currents.

8. In a load-break switch for service entrance and like applications inwhich the switch may be opened or closed under fault conditions, saidswitch including a stationary contact and a movable contact, saidmovable contact being movable along a given path into and out ofengagement with said stationary contact to open and close the switch,arc control apparatus comprising:

an arc-quencing chute, mounted in substantially encompassing relation tosaid path adjacent said stationary contact, for subdividing andextinguishing the are developed upon opening or closing of the switch;

a resilient cantilever-mounted arcing contact, electrical- UNITED STATESPATENTS 2,160,681 5/1939 Sandin 200147 6/1941 Graves 200144 1/1943Rawlins 20062 4/1955 Cellerini 200144 6/ 1958 Gieffers 20062 X 3/1965Jencks et a1. 200144 FOREIGN PATENTS 4/1964 Belgium. 10/1965 Germany.

ROBERT s. MACON, Primary Examiner.

US. Cl. X.R.

